Vibrating material sorting screens are used in a variety of applications, including sand and gravel businesses and in mining operations. Such vibrating screens are used to sort material size, and typically comprise an elongated deck, which slopes downwardly from the feed end to the material delivery end. Usually, the decks are mounted in a deck holding frame, which, in turn, is supported on springs extending to a platform on a support surface. An eccentric vibrator is employed to vibrate the frame on the springs to cause a shaking of the material poured onto the vibrating screen deck to facilitate the movement of the material down the deck, and to expedite the material separation. Both the aperture of the screen and the size of the deck determines the separation size of the materials, and any material which is larger than the screen aperture finally is supplied from the end of the deck to a suitable receptacle. All material which is smaller than the screen aperture falls through the deck for further separation or processing.
In some mining applications, the vibrating screen apparatus has two decks located one above the other, with the larger screen aperture on the top deck and a smaller screen aperture on the lower deck. In the sand and gravel business, three to five decks frequently are used, with the decks progressing in screen aperture from the largest at the top to the smallest at the bottom. Usually, all of these decks are mounted together in a single frame, vibrated by a single vibrating apparatus. The slope of each deck, from the feed end or material receiving end to the delivery end, is fixed once the vibrating screen apparatus is assembled. In addition, a single vibrating weight and drive motor is used; so that the magnitude and frequency of vibration of the entire unit is the same.
When a multiple deck vibrating screen unit is employed, the magnitude and frequency of the vibration necessarily is a compromise between the optimum magnitude and speed of vibration required for the deck separating the larger size materials and the magnitude and speed of vibration required for the deck which is separating the smaller sized materials. In addition, the rate at which materials traverse the deck from the feed end to the delivery end varies, depending upon the size of the material; so that a compromise generally is made in the slope of the decks during the manufacturing of a multiple deck unit. In some cases, the slope angle of the different decks can be made to vary relative to one another; but once the unit is made, the different slope angles cannot further be adjusted in a typical deck.
When multiple deck units having three or more decks are employed, the compromises, which must be reached between the slope or angle of the different decks and the magnitude and speed of the vibrator, result in ever greater departures from the optimum, which would be desired for each deck having a single screen size. In view of this, it is desirable to provide a vibrating screen apparatus for a multiple deck unit which may be operated with each deck vibrated independently of the others, and where the angle or slopes of the decks may be independently varied, as desired.